I don’t like vowels much. They are slippery little beasts. They wander about when you’re not looking. Give me a good, honest consonant any day.
There are some well-documented shifts in vowel quality going on now, and some that have been in progress for quite a time. One is the Northern Cities Shift in the USA.
Another is front vowel raising in NZ English, whereby the TRAP vowel is raised to about the quality of the GBE DRESS vowel, NZ DRESS sounds a lot like GBE KIT, and NZ KIT sounds like a raised schwa. The raising is even more extreme for some speakers. Almost 20 years ago in Wellington I was somewhat surprised at a shop assistant’s utterance as she handed me a $10 note in my change. She said: “Here’s your tiːn“. The well-known NZ SQUARE-NEAR merger used to result in a quality something like eə, but these days the quality is usually ɪə.
I think there is a chain shift going on in GBE too, but in the opposite direction to the NZ changes. The change in quality of the GOOSE vowel from u to ʉ, sometimes accompanied by unrounding, has been commented on for quite a few years now. I have recently been noticing younger speakers producing a vowel in <ing> endings which sounds very like the DRESS vowel, so for example shopping sounds a lot like ˈʃɒpeŋ. Finally, the DRESS vowel is often lowered to sound rather like æ, especially after w. I have lost count of the times weather forecasters have warned me of impending ˈwæt ˈwæðə. Put all these together and you get something like what is diagrammed below.